These calculators have become cheap enough (and I know, for a lot of people on a personal level a hundred bucks is not cheap, but on the market level, it is) that repairing them isn't worth it. By the time you pay shipping, parts, and labor you may as well have bought a new one.
As far as repairing goes, your best bet is to find a calculator for parts on eBay or Craigslist (because the screen isn't available by itself from TI), hope the screen isn't the problem in that unit, and try swapping out the screen yourself.
Sorry.